JP5319628B2 - Nitride semiconductor element and semiconductor optical device - Google Patents

Abstract

A nitride semiconductor device which improves the light emission efficiency is provided. The nitride semiconductor light emitting device includes the nitride semiconductor layer having a growth surface and the nitride semiconductor layer (layered structure) which is formed on the growth surface of the semiconductor layer, and includes an active layer that has a quantum well structure. The active layer includes a quantum well layer including the nitride semiconductor containing Al. Further, the growth surface of the semiconductor layer includes a plane having an off angle at least in an a axis direction with respect to an m-plane, and the off angle in the a axis direction is larger than an off angle in a c axis direction.

Description

  The present invention relates to a nitride semiconductor element and a semiconductor optical device on which the nitride semiconductor element is mounted.

  Nitride semiconductors typified by GaN, AlN, InN, and mixed crystals thereof have characteristics that they have a large band gap Eg and are direct transition type semiconductor materials compared to AlGaInAs semiconductors and AlGaInP semiconductors. Yes. For this reason, these nitride semiconductors constitute semiconductor light emitting devices such as a semiconductor laser device capable of emitting light in a wavelength range from ultraviolet to green and a light emitting diode device capable of covering a wide light emission wavelength range from ultraviolet to red. It is attracting attention as a material, and is widely considered for applications such as projectors, full-color displays, and environmental and medical fields.

  In recent years, semiconductor light emitting devices using nitride semiconductors can be applied in a very wide range of fields such as sterilization / water purification, various medical fields, and high-speed decomposition treatment of pollutants by shortening the emission wavelength. The research and development of semiconductor light-emitting elements that emit light in the ultraviolet region are being actively conducted by each research institution.

  In a semiconductor light emitting device using a nitride semiconductor, a sapphire substrate is generally used as a substrate. In addition, a c-plane ((0001) plane) that is a polar plane is used as the growth plane. A nitride semiconductor light emitting device is formed by laminating a nitride semiconductor layer including an active layer on the c-plane.

  However, in the semiconductor light emitting device as described above, there has been an inconvenience so far that it is difficult to improve the quality of AlN, AlGaN, and AlInGaN crystals. Therefore, there is a problem that it is difficult to improve the light emission efficiency of the light emitting element. As one of the causes, it is suggested that the surface migration of Al atoms is insufficient. And as countermeasures, proposals for a raw material supply method (for example, see Non-Patent Document 1) and the effectiveness of high-temperature growth (for example, see Non-Patent Document 2) have been proposed.

  Specifically, in Non-Patent Document 1 described above, when forming an AlN layer or an AlGaN layer having a high Al composition ratio, a group III atom source and a group V atom source are not supplied at the same time. A method of alternately supplying raw materials is used. Non-Patent Document 2 discloses that the crystal quality of the AlN layer is improved by growing the AlN layer on the c-plane sapphire substrate at a high temperature of 1400 ° C.

  In addition, when a substrate whose main surface is the c-plane that is a polar surface is used, the nitride semiconductor layer includes an active layer on the c-plane because the substrate has polarity in the normal direction (c-axis direction) of the main surface. When is laminated, spontaneous polarization occurs in the active layer. For this reason, when a substrate having a c-plane as a main surface is used, there is also a problem that the light emission efficiency is lowered due to spontaneous polarization. For this reason, a nitride semiconductor laser element using a substrate having a non-polar plane m-plane as the main plane instead of the plane having the c-plane as the main plane has also been proposed (see, for example, Patent Documents 1 and 2). .

JP 2009-158955 A JP 2009-123969 A

M.M. Hiroki and N.K. Kobayashi, “Flat Surfaces and Interfaces in AlN / GaN Heterostructures and Superstratics Growth by Flow-Rate Modulation Epitaxy”, Jpn. J. et al. Appl. Phys. 42 (2003) 2305. M.M. Imura, K .; Nakano, N .; Fujimoto, N .; Okada, K .; Balakrishnan, M .; Iwaya, S .; Kamiyama, H .; Amano, I .; Akasaki, T .; Noro, T .; Takagi, and A.A. Bando, “Dislocations in AlN Epilayers Growth on Sapphire Substrate by High-Temperature Metal-Organic Vapor Phase Epitaxy”, Jpn. J. et al. Appl. Phys. 46 (2007) 1458.

  However, even when the methods proposed in Non-Patent Documents 1 and 2 are used, the light emission efficiency is not sufficiently high, and there is still room for improvement of the light emission efficiency. In addition, crystal growth at a high temperature as proposed in Non-Patent Document 2 has a problem that the temperature load on the growth furnace is large.

  Also in Patent Documents 1 and 2, the luminous efficiency is not sufficiently high, and further improvement in luminous efficiency is required.

  The present invention has been made to solve the above-described problems, and one object of the present invention is to provide a nitride semiconductor device capable of improving luminous efficiency, and the nitride semiconductor device. A semiconductor optical device is provided.

  Another object of the present invention is to provide a nitride semiconductor element in which a nitride semiconductor layer with good flatness is formed, and a semiconductor optical device including the nitride semiconductor element.

  The inventors of the present application conducted various experiments paying attention to the above problems and, as a result of intensive studies, formed a nitride semiconductor layer on a semiconductor layer whose growth surface is a surface having an off angle with respect to the m-plane. As a result, it has been found that the crystal quality can be improved.

  That is, the nitride semiconductor device according to the first aspect of the present invention includes a growth surface, a semiconductor layer made of a nitride semiconductor, and an active layer formed on the growth surface of the semiconductor layer and having a quantum well structure. And a nitride semiconductor layer. The active layer includes a quantum well layer made of a nitride semiconductor containing Al. The growth surface of the semiconductor layer is composed of a surface having an off angle at least in the a-axis direction with respect to the m-plane. The a-axis direction off-angle is configured to be larger than the c-axis direction off-angle.

  In the nitride semiconductor device according to the first aspect, as described above, a surface having an off angle at least in the a-axis direction with respect to the m-plane is formed on the growth surface of the semiconductor layer. The crystal quality of the nitride semiconductor layer can be improved. For this reason, also in the quantum well layer included in the nitride semiconductor layer, the crystal quality can be improved. Thereby, luminous efficiency can be improved.

  In the first aspect, the planarity of the nitride semiconductor layer formed on the growth surface is improved by making the off-angle in the a-axis direction on the growth surface larger than the off-angle in the c-axis direction. Can do. For this reason, the luminous efficiency can be improved also by this. In addition, since the in-plane layer thickness distribution can be made uniform by improving the flatness of the nitride semiconductor layer, the occurrence of cracks and variations in element resistance due to the non-uniform in-plane layer thickness distribution. In addition, uneven current injection can be suppressed.

  Furthermore, in the first aspect, by configuring as described above, the crystal quality and flatness of the nitride semiconductor layer can be improved without growing the nitride semiconductor layer at a high temperature. For this reason, the temperature load to the growth furnace can also be reduced.

  In the first aspect, the growth surface of the semiconductor layer is composed of a surface having an off angle at least in the a-axis direction with respect to the m-plane. Can suppress the occurrence of spontaneous polarization. For this reason, the fall of the luminous efficiency resulting from spontaneous polarization can also be suppressed.

  In the nitride semiconductor device according to the first aspect, preferably, the off angle in the a-axis direction and the off angle in the c-axis direction are each greater than 0.1 degree. If comprised in this way, while being able to improve the crystal quality of a nitride semiconductor layer easily, flatness can be improved easily.

  In the nitride semiconductor device according to the first aspect, it is more preferable that the off angle in the a-axis direction is larger than 0.1 degree and not larger than 10 degrees. By setting the off angle in the a-axis direction to an angle within such a range, an effect of improving the crystal quality and an effect of improving the flatness can be effectively obtained.

  In the nitride semiconductor device according to the first aspect, it is further preferable that the off angle in the a-axis direction is greater than 1 degree and less than or equal to 10 degrees. Thus, by setting the off angle in the a-axis direction to an angle larger than 1 degree, it is possible to more effectively obtain the effect of improving the crystal quality and the effect of improving the flatness.

In the nitride semiconductor device according to the first aspect, the quantum well layer is a semiconductor represented by a composition formula of Al _x1 In _y1 Ga _1-x1-y1 N (0 <x1 ≦ 1, 0 ≦ y1 ≦ 1). It is preferable that it is comprised from these.

  In this case, the Al composition ratio X1 of the quantum well layer is preferably in the range of 0.15 ≦ x1 ≦ 0.90. If the Al composition ratio X1 of the quantum well layer is in such a range, the light emission efficiency can be more effectively improved. The Al composition ratio X1 of the quantum well layer is preferably 0.3 or more, and more preferably 0.5 or more. Thus, by setting the Al composition ratio X1 of the quantum well layer to 0.15 or more, the m-plane has an off angle at least in the a-axis direction, and the off-angle in the a-axis direction is c When a growth surface configured to be larger than the off-angle in the axial direction is used, when compared with a surface using another surface other than the above surface (for example, c-plane), other surface (for example, c The effect of improving the luminous efficiency with respect to the surface) can be increased. Further, if the Al composition ratio X1 of the quantum well layer is 0.3 or more, the effect of improving the light emission efficiency with respect to other surfaces (for example, c-plane) can be further increased, and if the Al composition ratio X1 is 0.5 or more. The effect of improving the light emission efficiency with respect to other surfaces (for example, c-plane) can be further increased. Further, carrier confinement can be made possible by setting the Al composition ratio X1 of the quantum well layer to 0.9 or less.

In the case where the quantum well layer is composed of a semiconductor represented by the composition formula of Al _x1 In _y1 Ga _{1-x1 -y1} N, the In composition ratio y1 of the quantum well layer is 0.00 ≦ y1 ≦ 0. It is preferably in the range of 12. That is, the quantum well layer may be configured to include In or may be configured not to include In. When the quantum well layer contains In, it is possible to grow a quantum well layer excellent in flatness at a relatively low temperature. For this reason, the temperature load to the growth furnace (crystal growth apparatus) can be reduced effectively. In addition, since the number of parameters for controlling strain increases when forming the element structure, the degree of freedom in designing the element can be increased. In addition, when the In composition ratio y1 is 0.12 or less, a crystal having excellent flatness can be easily realized. On the other hand, when the quantum well layer does not contain In, such a quantum well layer is formed on a semiconductor layer whose growth surface is a surface having an off-angle in the a-axis direction, thereby improving the crystal quality and The improvement effect of flatness can be remarkably obtained.

  In the nitride semiconductor device according to the first aspect, the semiconductor layer having a growth surface is preferably composed of a nitride semiconductor containing Al. In this case, the Al composition ratio of the semiconductor layer is preferably larger than the Al composition ratio of the quantum well layer, and the Al composition ratio is preferably 0.20 or more and 1.00 or less. If comprised in this way, while being able to improve the crystal quality of a nitride semiconductor layer, it can suppress that the light from an active layer is absorbed by this semiconductor layer. The Al composition ratio of the semiconductor layer is more preferably 0.3 or more, and further preferably 0.5 or more.

In the nitride semiconductor device according to the first aspect, preferably, the active layer is represented by a composition formula of Al _x2 In _y2 Ga _1-x2-y2 N (0 <x2 ≦ 1, 0 ≦ y2 ≦ 1). The Al composition ratio x2 of the barrier layer is larger than the Al composition ratio of the quantum well layer. If comprised in this way, the band gap of a barrier layer will become larger than the band gap of a quantum well layer.

  In this case, the Al composition ratio x2 of the barrier layer is preferably in the range of 0.20 ≦ x2 ≦ 1.00. With this configuration, the band gap of the barrier layer is larger than the band gap of the quantum well layer, so that carriers can be effectively confined in the quantum well and absorption of light emitted from the active layer is suppressed. can do. The Al composition ratio x2 of the barrier layer is more preferably 0.3 or more, and further preferably 0.5 or more.

The barrier layer is made of a semiconductor expressed by a composition formula of Al _x2 In _y2 Ga _1-x2-y2 N, and the quantum well layer is made of Al _x1 In _y1 Ga _1-x1-y1 N (0 ≦ x1). ≦ 1, 0 ≦ y1 ≦ 1), the In composition ratio y2 of the barrier layer is smaller than the In composition ratio y1 of the quantum well layer, and 0.00 It is preferable to be in the range of ≦ y2 ≦ 0.08. That is, the barrier layer may be configured to include In or may not be configured to include In. In either case, the band gap of the barrier layer is preferably configured to be larger than the band gap of the quantum well layer. When the barrier layer contains In, it is possible to grow a barrier layer excellent in flatness at a relatively low temperature. For this reason, the temperature load to the growth furnace (crystal growth apparatus) can be reduced effectively. In addition, when the element structure is formed, the number of parameters for controlling the distortion increases, so that the degree of freedom in design can be increased. In addition, by setting the In composition ratio y1 to 0.08 or less, a crystal having excellent flatness can be easily realized. Furthermore, the In composition ratio y2 of the barrier layer is made smaller than the In composition ratio y1 of the quantum well layer so that the band gap of the barrier layer becomes larger than the band gap of the quantum well layer. For this reason, the influence of the light absorption in an active layer can be suppressed. On the other hand, when the barrier layer does not contain In, such a quantum well layer is formed on the semiconductor layer whose growth surface is a surface having an off-angle in the a-axis direction, thereby improving the crystal quality and improving the flatness. The effect of improving the property can be obtained remarkably.

  In the configuration in which the active layer includes a barrier layer, the barrier layer is preferably made of AlGaN or AlInGaN.

  In the nitride semiconductor device according to the first aspect, the quantum well layer is preferably made of AlGaN or AlInGaN.

  In the nitride semiconductor device according to the first aspect, an AlN layer may be formed on the growth surface of the semiconductor layer so as to be in contact with the growth surface. Thus, by forming the AlN layer so as to be in contact with the growth surface of the semiconductor layer, an AlN layer having excellent crystallinity and flatness can be formed. For this reason, by laminating a semiconductor layer on the AlN layer, the crystallinity and flatness of the semiconductor layer laminated on the AlN layer can be improved.

  In the nitride semiconductor device according to the first aspect, preferably, the nitride semiconductor layer formed on the growth surface of the semiconductor layer includes an n-side nitride semiconductor layer formed on the semiconductor layer side with respect to the active layer. The active layer further includes a p-side nitride semiconductor layer formed on the opposite side of the n-side nitride semiconductor layer, and the n-side nitride semiconductor layer does not include a GaN layer. If comprised in this way, a favorable surface morphology can be obtained.

  In the nitride semiconductor device according to the first aspect, the wavelength of light emitted from the active layer is preferably 240 nm or more and 360 nm or less. If comprised in this way, the light emitting element which emits the light of an ultraviolet region and has high luminous efficiency can be obtained.

  In this case, it is more preferable that the wavelength of light emitted from the active layer is 260 nm or more and 300 nm or less.

  In the nitride semiconductor device according to the first aspect, the semiconductor layer having a growth surface is preferably composed of any one of AlGaN, AlInGaN, and AlN.

  The nitride semiconductor device according to the first aspect may further include a substrate constituting a semiconductor layer having a growth surface. In this case, the substrate is preferably composed of any one of an AlGaN substrate, an AlInGaN substrate, and an AlN substrate. If comprised in this way, while being able to improve the crystal quality of the nitride semiconductor layer formed on a board | substrate, the flatness of a nitride semiconductor layer can be improved.

  In the nitride semiconductor device according to the first aspect, the substrate constituting the semiconductor layer having the growth surface may be composed of a GaN substrate. As described above, when a GaN substrate is used as the substrate, unlike the sapphire substrate, the substrate has conductivity, so that the degree of freedom in designing the element can be increased. In addition, if a GaN substrate is used as the substrate, a difference in thermal expansion coefficient and a difference in lattice constant from the nitride semiconductor layer formed on the substrate can be reduced as compared with the case where a sapphire substrate is used.

  The nitride semiconductor device according to the first aspect includes a template substrate in which the semiconductor layer is formed on a base substrate, and a nitride semiconductor layer including an active layer is formed on the template substrate. You can also.

  A semiconductor optical device according to a second aspect of the present invention is a semiconductor optical device on which the nitride semiconductor element according to the first aspect is mounted.

  As described above, according to the present invention, it is possible to easily obtain a nitride semiconductor element capable of improving the light emission efficiency and a semiconductor optical device including the nitride semiconductor element.

  Furthermore, according to the present invention, a nitride semiconductor element in which a nitride semiconductor layer with good flatness is formed, and a semiconductor optical device including the nitride semiconductor element can be easily obtained.

It is a schematic diagram (a figure showing a unit cell) for explaining a crystal structure of a nitride semiconductor. It is a schematic diagram for demonstrating the off angle of the growth surface of a nitride semiconductor layer. 1 is a cross-sectional view illustrating a nitride semiconductor light emitting device according to a first embodiment of the present invention. 1 is a cross-sectional view of a template substrate used in a nitride semiconductor light emitting device according to a first embodiment of the present invention. FIG. 3 is a cross-sectional view illustrating a configuration of an active layer of the nitride semiconductor light emitting device according to the first embodiment of the present invention. 1 is a cross-sectional view schematically showing a semiconductor optical device according to a first embodiment of the present invention. FIG. 6 is a cross-sectional view illustrating a nitride semiconductor light emitting device according to a second embodiment of the present invention. It is sectional drawing which showed the layer structure of the nitride semiconductor light-emitting device by 3rd Embodiment of this invention. FIG. 6 is a cross-sectional view illustrating a nitride semiconductor light emitting device according to a fourth embodiment of the present invention. It is sectional drawing of the template board | substrate used for the nitride semiconductor light-emitting device by 4th Embodiment of this invention. FIG. 7 is a cross-sectional view illustrating a nitride semiconductor light emitting device according to a fifth embodiment of the present invention. FIG. 7 is a cross-sectional view showing a nitride semiconductor light emitting device according to a sixth embodiment of the present invention. It is sectional drawing which showed the nitride semiconductor light-emitting device by the modification of 6th Embodiment. 1 is a cross-sectional view showing a nitride semiconductor light emitting device according to Example 1. FIG. 3 is a cross-sectional view showing a configuration of an active layer of a nitride semiconductor light emitting device according to Example 1. FIG. 6 is a cross-sectional view showing a nitride semiconductor light emitting device according to Example 2. FIG. 6 is a cross-sectional view showing a configuration of an active layer of a nitride semiconductor light emitting device according to Example 2. FIG. FIG. 6 is a cross-sectional view of an evaluation structure used for confirming the effect of improving the light emission efficiency of the nitride semiconductor light emitting device according to Example 2. It is sectional drawing which showed the semiconductor substrate by 7th Embodiment of this invention.

  Prior to describing specific embodiments of the present invention, knowledge obtained by various studies by the inventors will be described.

  The inventors of the present application have grown a nitride semiconductor layer containing Al on a nitride semiconductor layer whose growth surface is m-plane, and then nitrided Al containing it on the nitride semiconductor whose growth surface is c-plane. It has been found that the crystal quality is improved as compared with the case where the physical semiconductor layer is grown. This is because the migration of group III atoms reaching the crystal surface is longer on the nitride semiconductor layer with the m-plane as the growth surface than on the nitride semiconductor layer with the c-plane as the growth surface. It is guessed.

  At this time, as the Al composition ratio of the nitride semiconductor layer grown on the growth surface is larger, the m-plane has an off angle in at least the a-axis direction, and the off-angle in the a-axis direction is c-axis. When a growth surface configured to be larger than the off-angle of the direction is used, the effect of improving the crystal quality is large when compared with a surface using a surface other than the above surface (for example, c-plane). The tendency to become was seen. Specifically, the Al composition ratio of the nitride semiconductor layer containing Al is 15% or more, and the effect of improving the crystal quality with respect to the other surface (for example, c-plane) is large. . As the Al composition ratio increases, the effect of improving the crystal quality with respect to other planes (for example, c-plane) is increased because the Al diffusion constant is smaller than the Ga diffusion constant. This is presumably because the influence of Al atoms is increased, and the effect of prolonging the migration appears greatly.

  However, when a nitride semiconductor layer containing Al is grown on a nitride semiconductor layer having an m-plane as a growth surface, there is a disadvantage that pyramidal protrusions are generated on the growth surface. The pyramidal protrusions tended to become more prominent as the Al composition ratio of the nitride semiconductor layer grown on the growth surface was larger. Specifically, when the Al composition ratio is greater than 15% (0.15), pyramidal protrusions begin to appear prominently, and the flatness of the growth surface deteriorates. When the Al composition ratio is 30% (0.30) or more, the flatness of the growth surface is further deteriorated.

  For this reason, the unevenness of the growth surface is increased by the pyramidal protrusions. If the unevenness of the growth surface becomes large, the variation in the layer thickness becomes large, which may induce the generation of cracks. In addition, since the in-plane layer thickness distribution deteriorates, there are problems such as variations in element resistance in the layer direction and nonuniform current injection in the in-plane direction. For this reason, problems such as a decrease in luminous efficiency and an increase in element resistance occur.

  As described above, when a nitride semiconductor layer containing Al is grown on a nitride semiconductor layer having an m-plane as a growth surface, increasing the Al composition ratio improves the crystal quality, but increases the pyramid shape. It has been found that there is a problem that the flatness is lowered due to the generation of the portion.

  Thus, the inventors of the present application have made extensive studies and found that the above-mentioned problems can be solved by making a growth surface a surface having an off angle at least in the a-axis direction with respect to the m-plane. That is, a pyramid-shaped convex portion is generated by growing a nitride semiconductor layer containing Al on a nitride semiconductor layer whose growth surface is a surface having an off angle at least in the a-axis direction with respect to the m-plane. It has been found that the crystal quality can be improved without any problems. In this case, by making the off angle in the a-axis direction larger than the off angle in the c-axis direction, it is possible to effectively suppress the generation of pyramid-shaped convex portions.

  Also, if the growth surface of the nitride semiconductor layer is configured as described above, it is possible to maintain good flatness of the growth surface by increasing the Al composition ratio of the nitride semiconductor layer formed on the growth surface. However, it has been found that the crystal quality can be improved. Therefore, the nitride semiconductor layer having such a growth surface is suitable for a nitride semiconductor light emitting element that emits light in the ultraviolet region, which requires a nitride semiconductor layer having a high Al composition ratio.

  The reason why the crystal quality improvement effect can be obtained is presumed to be because the migration of Al is extended as described above. One of the reasons why the flatness improvement effect can be obtained is that the growth surface of the nitride semiconductor layer has an off-angle at least in the a-axis direction with respect to the m-plane, thereby causing the migration of group III atoms. It is presumed that the direction changes.

  Therefore, by configuring as described above, the crystal quality and flatness can be improved, and thus the light emission efficiency can be improved. In addition, it has been found that suppression of crack generation and reduction of element resistance can be realized.

  Furthermore, as a result of investigations by the inventors of the present application, an element structure is formed on the growth surface using a nitride semiconductor layer having a growth surface that has an off angle at least in the a-axis direction with respect to the m-plane. In this case, it has been found that the growth temperature of the p-type nitride semiconductor layer can be lowered.

  Specifically, when the inventors of the present invention have grown a p-type nitride semiconductor layer at a temperature lower than 900 ° C. and made a comparison, a nitride semiconductor layer having a c-plane which is a polar plane as a growth plane (for example, In the case of using a c-plane GaN substrate), it was confirmed that many defects due to threading dislocations occurred on the surface of the p-type nitride semiconductor layer. In this case, it was confirmed that the size of defects generated on the surface also increased. When observing defects generated on the surface, observation is usually difficult unless a scanning electron microscope (SEM) or the like is used. However, when a GaN substrate having a c-plane as a growth surface is used, a defect that is large enough to be observed even when an optical microscope with a magnification of about 200 to 800 times is used occurs. This is considered to be because the crystallinity deteriorates because the migration of atoms is suppressed because the growth temperature is low. Nitride semiconductors tend to exhibit n-type conduction, but tend to exhibit p-type conduction. For this reason, when the nitride semiconductor layer is grown at a low temperature, p-type conduction is not exhibited due to deterioration of crystallinity. In particular, an AlGaN type nitride semiconductor layer containing Al is required to have a higher growth temperature than a GaN type nitride semiconductor layer containing no Al. In addition, when the Al composition ratio is high, high-temperature growth at about 1200 ° C. is required to improve crystal quality.

  On the other hand, when a nitride semiconductor layer (for example, an m-plane GaN substrate) having a plane having an off angle at least in the a-axis direction with respect to the m-plane as a growth plane is used, nitridation using the c-plane as a growth plane Compared with the case where the physical semiconductor layer was used, a flat and good crystal surface was observed. Moreover, when the electrical characteristics were measured, it showed good p-type conduction.

  The reason why such an effect is obtained is considered to be that migration of atoms is sufficiently ensured even when the growth temperature is set low.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments embodying the present invention will be described in detail with reference to the drawings. In the following embodiments, an example in which the present invention is applied to a nitride semiconductor light emitting element (light emitting diode element) which is an example of a nitride semiconductor element will be described. In the following embodiments, a “nitride semiconductor” refers to a semiconductor made of Al _x Ga _y In _z N (0 ≦ x ≦ 1; 0 ≦ y ≦ 1; 0 ≦ z ≦ 1; x + y + z = 1). means.

(First embodiment)
FIG. 1 is a schematic diagram for explaining a crystal structure of a nitride semiconductor. FIG. 2 is a schematic diagram for explaining the off-angle of the growth surface of the nitride semiconductor layer. FIG. 3 is a cross-sectional view illustrating the nitride semiconductor light emitting device according to the first embodiment of the present invention. 4 to 6 are views for explaining the nitride semiconductor light emitting device according to the first embodiment of the present invention. First, the configuration of the nitride semiconductor light emitting device 500 according to the first embodiment of the present invention will be described with reference to FIGS.

  The nitride semiconductor constituting the nitride semiconductor light emitting device 500 according to the first embodiment has a hexagonal crystal structure as shown in FIG. In this crystal structure, a plane (upper surface of the hexagonal column) whose normal is the c-axis [0001] of the hexagonal crystal that can be regarded as a hexagonal column is called a c-plane (0001), and each side wall surface of the hexagonal column is an m-plane {1 -100}. In the nitride semiconductor, since there is no symmetry plane in the c-axis direction, the polarization direction is along the c-axis direction. For this reason, the c-plane exhibits different properties on the + c axis side and the −c axis side. That is, the + c plane ((0001) plane) and the −c plane ((000-1) plane) are not equivalent planes, and have different chemical properties. On the other hand, since the m-plane is a crystal plane perpendicular to the c-plane, the normal of the m-plane is orthogonal to the polarization direction. For this reason, the m-plane is a nonpolar plane with no polarity. As described above, since each of the side wall surfaces of the hexagonal column is an m-plane, the m-plane has six types of plane orientations ((1-100), (10-10), (01-10), ( −1100), (−1010), and (0−110)), these plane orientations are plane orientations equivalent to crystal geometry, and hence are collectively referred to as {1-100}. Show.

  In addition, the nitride semiconductor light emitting device 500 according to the first embodiment includes the nitride semiconductor layer 20 having the growth surface 20a, as shown in FIGS. The growth surface 20a of the nitride semiconductor layer 20 is a surface having off angles in the a-axis direction ([11-20] direction) and the c-axis direction (c-axis [0001] direction) with respect to the m-plane. Further, the off angle in the a-axis direction on the growth surface 20a is configured to be larger than the off-angle in the c-axis direction. The nitride semiconductor layer 20 is an example of the “semiconductor layer having a growth surface” in the present invention.

  Here, with reference to FIG. 2, a GaN layer is taken as an example of the nitride semiconductor layer 20 having the growth surface 20a, and the off angles in the a-axis direction and the c-axis direction will be described in more detail. First, two crystal axis directions of an a-axis [11-20] direction and a c-axis [0001] direction are defined with respect to the m-plane. These a-axis and c-axis are perpendicular to each other, and are also perpendicular to the m-axis. Further, when the crystal axis vector of the GaN layer 5 matches the normal vector of the layer surface (growth surface 5a) (when the off-angle becomes 0 with respect to all directions), the a-axis direction and the c-axis direction The directions parallel to the m-axis direction are defined as an X direction, a Y direction, and a Z direction, respectively. Next, consider a first surface having a normal in the Y direction and a second surface having a normal in the X direction. The crystal axis vectors that appear when the crystal axis vector is projected onto the first surface and the second surface are defined as a first projection vector and a second projection vector, respectively. At this time, an angle θa formed by the first projection vector and the normal vector is an off angle in the a-axis direction, and an angle θc formed by the second projection vector and the normal vector is an off-angle in the c-axis direction. The off-angle in the a-axis direction has the same characteristics in the + direction and the − direction because the + direction and the − direction have the same surface state in terms of crystal. For this reason, it can describe with an absolute value. On the other hand, the c-axis direction is a + direction and a − direction, and there are cases where the Ga polar surface becomes stronger and the N polarity surface becomes stronger, and the characteristics differ depending on the direction. Separately described.

  In the first embodiment, as shown in FIG. 4, the nitride semiconductor layer 20 is formed on a nitride semiconductor substrate 10 as a base substrate. Similar to the growth surface 20a of the nitride semiconductor layer 20, the growth surface 10a of the nitride semiconductor substrate 10 is a surface having off-angles in the a-axis direction and the c-axis direction with respect to the m-plane. Further, the off angle in the a-axis direction on the growth surface 10a is configured to be larger than the off-angle in the c-axis direction. A template substrate 30 is configured by the nitride semiconductor layer 20 and the nitride semiconductor substrate 10.

  As the nitride semiconductor substrate 10, for example, a GaN substrate, an AlGaN substrate, an AlInGaN substrate, an AlN substrate, or the like can be used. The nitride semiconductor layer 20 having the growth surface 20a is configured using a nitride semiconductor containing Al (for example, AlGaN, AlInGaN, AlN). In this case, the Al composition ratio of the nitride semiconductor layer 20 is preferably larger than the Al composition ratio of a quantum well layer 120a (see FIG. 5) described later and in the range of 0.20 or more and 1.00 or less. . The Al composition ratio of the nitride semiconductor layer 20 is more preferably 0.30 or more, and further preferably 0.50 or more.

  When a GaN substrate is used as the nitride semiconductor substrate 10, the GaN substrate has conductivity unlike a sapphire substrate, so that the degree of freedom in device design is increased. In addition, compared to the case of using a different substrate such as a sapphire substrate, the difference in thermal expansion coefficient and lattice constant from the AlInGaN material is small, so that it is suitable for forming an AlInGaN layer. However, since the GaN substrate absorbs ultraviolet light, it needs to be designed in consideration of light absorption.

  When an AlGaN substrate is used as the nitride semiconductor substrate 10, the Al composition ratio of the AlGaN substrate is set higher than the Al composition ratio of the quantum well layer 120a (see FIG. 5), thereby suppressing the influence of light absorption. . For this reason, unlike the case of using a GaN substrate, the design in consideration of light absorption becomes unnecessary, and the design freedom of the element structure is increased. Furthermore, if the Al composition ratio of the AlGaN substrate is adjusted so that the lattice constant is close to that of the AlInGaN material constituting the light emitting element, a crack suppressing effect can also be expected. In this case, it is preferable that the multilayer constant (each nitride semiconductor layer) constituting the element structure be close to the lattice constant of the thickest layer.

  In addition, when an AlGaN substrate is used as the nitride semiconductor substrate 10, the degree of freedom of the lattice constant of the substrate is increased, so that the degree of freedom of design of the nitride semiconductor constituting the light emitting element is increased.

  Further, when an AlN substrate is used for the nitride semiconductor substrate 10, in addition to the same effect as that of the AlGaN substrate, the heat dissipation is improved, so that the light emission characteristics can be improved.

  Here, in the growth surface 20a of the nitride semiconductor layer 20, the off angle in the a-axis direction and the off angle in the c-axis direction are each configured to be larger than 0.1 degrees. Further, it is more preferable that the off-angle in the a-axis direction is configured to be greater than 0.1 degree and 10 degrees or less. More preferably, the angle is greater than 1.0 degree and 10 degrees or less. In addition, the growth surface 10a of the nitride semiconductor substrate 10 is preferably configured in the same manner as described above.

  A nitride semiconductor layer 200 (layer structure 200) including the active layer 120 is formed on the growth surface 20a of the nitride semiconductor layer 20. The nitride semiconductor layer 200 is configured by stacking a plurality of semiconductor layers, and includes an n-side nitride semiconductor layer 210 and a p-side nitride semiconductor layer 220. The n-side nitride semiconductor layer 210 and the p-side nitride semiconductor layer 220 are formed so as to sandwich the active layer 120. In the first embodiment, the n-side nitride semiconductor layer 210 does not include a GaN layer.

  Specifically, as shown in FIG. 3, an n-type AlInGaN layer 110 having a thickness of about 1.5 μm to about 2.0 μm is formed on the growth surface 20a of the nitride semiconductor layer 20, for example. . The active layer 120 is formed on the n-type AlInGaN layer 110. On the active layer 120, for example, a carrier block layer 130 made of p-type AlInGaN having a thickness of about 15 nm is formed. On the carrier block layer 130, for example, a p-type AlInGaN layer 140 having a thickness of about 10 nm is formed. On the p-type AlInGaN layer 140, for example, a p-type contact layer 150 made of p-type AlInGaN having a thickness of about 50 nm is formed. The p-type contact layer 150 may be made of AlGaN or GaN.

As shown in FIG. 5, the active layer 120 has a quantum well structure in which barrier layers 120b and quantum well layers 120a are alternately stacked. The quantum well layer 120a constituting the active layer 120 is composed of a semiconductor layer represented by a composition formula of Al _x1 In _y1 Ga _1-x1-y1 N (0 <x1 ≦ 1, 0 ≦ y1 ≦ 1). . The barrier layer 120b is composed of a semiconductor layer represented by a composition formula of Al _x2 In _y2 Ga _1-x2-y2 N (0 <x2 ≦ 1, 0 ≦ y2 ≦ 1), and the Al composition ratio x2 is larger than the Al composition ratio x1 of the quantum well layer 120a.

  The Al composition ratio x1 of the quantum well layer 120a is preferably in the range of 0.15 ≦ x1 ≦ 0.90, and more preferably in the range of 0.30 ≦ x1 ≦ 1.00. More preferably, it is in the range of 0.50 ≦ x1 ≦ 1.00. The In composition ratio y1 is preferably in the range of 0.00 ≦ y1 ≦ 0.12.

  The Al composition ratio x2 of the barrier layer 120b is preferably in the range of 0.20 ≦ x2 ≦ 1.00. The Al composition ratio x2 of the barrier layer 120b is more preferably in the range of 0.30 ≦ x2 ≦ 1.00. More preferably, it is in the range of 0.50 ≦ x2 ≦ 1.00. The In composition ratio y2 is preferably in the range of 0.00 ≦ y2 ≦ 0.08.

  The quantum well layer 120a may be made of AlInGaN containing In or may be made of AlGaN not containing In. Similarly, the barrier layer 120b may be made of AlInGaN containing In or may be made of AlGaN not containing In. When the barrier layer 120b contains In, the In composition ratio y2 is preferably configured to be smaller than the In composition ratio y1 of the quantum well layer 120a.

  Note that the Al composition ratio and the In composition ratio of the n-type AlInGaN layer 110 may be set to be the same as those of the barrier layer 120b. Although the composition ratio of the n-type AlInGaN layer 110 and the barrier layer 120b may be different, it is preferable to set the same as described above because the lattice mismatch difference at the interface is eliminated. When the compositions are different, the band gap of the n-type AlInGaN layer 110 is preferably configured to be larger than the band gap of the barrier layer 120b. With such a configuration, carriers can be effectively confined in the active layer 120.

  Further, the Al composition ratio and the In composition ratio of the p-type AlInGaN layer 140 may be set to be the same as those of the barrier layer 120b, similarly to the n-type AlInGaN layer 110. The composition ratio of the p-type AlInGaN layer 140 and the barrier layer 120b may be different.

  In the first embodiment, as shown in FIG. 3, the nitride semiconductor light emitting element 500 is configured as a light emitting diode element having a so-called lateral structure. For this reason, a part of the nitride semiconductor layer 200 (layer structure 200) formed on the template substrate 30 is dug up to a depth in the middle of the n-type AlInGaN layer 110 from the p-type contact layer 150 by dry etching or the like. ing. An n-side electrode 170 is formed on the bottom surface of the dug portion (n-type AlInGaN layer 110). The n-side electrode 170 is made of, for example, an Al electrode or an Ag / Cu electrode having a multilayer structure in which an Ag layer and a Cu layer are sequentially stacked from the substrate side. On the other hand, a p-side electrode 160 is formed on the p-type contact layer 150. The p-side electrode 160 is composed of, for example, a Ni / Au electrode having a multilayer structure in which an Ni layer (not shown) and an Au layer (not shown) are sequentially laminated from the p-type contact layer 150 side. Thus, in the first embodiment, the p-side electrode 160 and the n-side electrode 170 are formed on the upper surface side (growth surface 20a side) of the template substrate 30 (nitride semiconductor layer 20). In addition, the metal used for the electrode is only an example, and is not limited to the above example.

  As described above, in the nitride semiconductor light emitting device 500 according to the first embodiment, the quantum well layer 120a is formed of a nitride semiconductor containing Al, thereby forming a light emitting diode device that emits ultraviolet light (deep ultraviolet light). Has been. The wavelength of light emitted from the active layer 120 is preferably 240 nm or more and 360 nm or less, and more preferably 250 nm or more and 320 nm or less. Moreover, it is more preferable if it is 260 nm or more and 300 nm or less. When the wavelength of light emitted from the active layer 120 is 240 nm or more, the energy difference between the heterointerfaces such as the quantum well layer 120a and the barrier layer 120b is large to some extent, and the carrier confinement effect is increased. Moreover, it is preferable that the wavelength of light is 360 nm or less because the material of the active layer 120 is made of AlInGaN. In addition, when the wavelength of light is 250 nm or more, the barrier of the carrier block layer 130 provided between the active layer 120 and the p-type contact layer 150 can be set relatively high with respect to the quantum well layer 120a. Becomes larger. In addition, when the wavelength of light is 320 nm or less, the Al composition ratio of the quantum well layer 120a and the barrier layer 120b becomes higher than about 30%, and the effect of improving the crystal quality with respect to other surfaces (for example, c-plane) becomes large. When the wavelength of light emitted from the active layer 120 is in the range of 260 nm to 300 nm, the carrier confinement effect and the like can be obtained more effectively.

  Further, the nitride semiconductor light emitting device 500 configured as described above is mounted on a can-type package 1000a and configured in the semiconductor optical device 1000 as shown in FIG.

  In the first embodiment, as described above, the growth surface 20a of the nitride semiconductor layer 20 is configured from a surface having off-angles in the a-axis direction and the c-axis direction with respect to the m-plane, and in the a-axis direction. By making the off angle larger than the off angle in the c-axis direction, the crystal quality of each of the nitride semiconductor layers 110 to 150 formed on the growth surface 20a can be improved. Therefore, the light emission efficiency of the nitride semiconductor light emitting device 500 can be improved. Further, if configured as described above, it is possible to effectively generate the pyramidal protrusions observed when the nitride semiconductor layer containing Al is formed on the nitride semiconductor layer whose growth surface is the m-plane. Can be suppressed. Therefore, a good surface morphology can be obtained, and the flatness of each nitride semiconductor layer 110-150 can be improved. As a result, the in-plane layer thickness distribution can be made uniform, so that the generation of cracks, variation in element resistance, non-uniformity in current injection, etc., caused by the non-uniform in-plane layer thickness distribution can be suppressed. it can.

  Note that by using the nitride semiconductor layer 20 having the growth surface 20a, the flatness and crystallinity of each of the nitride semiconductor layers 110 to 150 containing Al formed on the growth surface 20a can be improved. Further, not only the active layer 120 but also the n-type AlInGaN layer 110, the carrier block layer 130, the p-type AlInGaN layer 140, and the p-type contact layer 150 can improve flatness and crystallinity.

  The n-type AlInGaN layer 110, the carrier block layer 130, the p-type AlInGaN layer 140, and the p-type contact layer 150 preferably have an Al composition ratio of 0.20 to 1.00. In the carrier block layer 130, the Al composition ratio is preferably larger than the Al composition ratio x2 of the barrier layer 120b and in the range of 0.50 to 1.00. The Al composition ratio of the carrier block layer 130 is more preferably in the range of 0.70 or more and 1.00 or less. If the carrier block layer 130 is configured in this manner, carriers can be effectively confined in the active layer 120.

  In the first embodiment, the crystal quality and flatness can be easily improved by setting the off-angle in the a-axis direction to an angle larger than 0.1 degree on the growth surface 20a of the nitride semiconductor layer 20. it can. Moreover, crystal quality and flatness can be further improved by setting the off angle in the a-axis direction to an angle larger than 0.1 degree. As the off angle in the a-axis direction increases, the amount of In taken in tends to decrease. Therefore, when a nitride semiconductor layer containing In (for example, an AlInGaN layer) is formed on the growth surface 20a. From the viewpoint of raw material efficiency, the absolute value of the off angle in the a-axis direction is preferably 10 degrees or less as described above. As described above, by setting the off angle in the a-axis direction on the growth surface 20a to be in the range of greater than 0.1 degrees and less than or equal to 10 degrees, the surface morphology of each of the nitride semiconductor layers 110 to 150 composed of the AlInGaN layer is improved. Can be. That is, the effect of improving the surface morphology is obtained. In addition, the operating voltage of the nitride semiconductor light emitting device 500 can be reduced.

  Further, according to the study by the inventors of the present application, when each nitride semiconductor layer containing Al is formed on the growth surface 20a of the nitride semiconductor layer 20 having the above configuration, the larger the Al composition ratio, the larger the m plane. On the other hand, when a growth surface that has an off angle in at least the a-axis direction and is configured so that the off-angle in the a-axis direction is larger than the off-angle in the c-axis direction is used. The effect of improving the crystal quality with respect to those using other surfaces (for example, c-plane) is increased. In addition, a surface having an off-angle outside the specified range of the m-plane (for example, a surface having no off-angle in the a-axis direction or a surface having an off-angle in the c-axis direction larger than the off-angle in the a-axis direction). The improvement effect of the flatness with respect to what was used becomes large. Specifically, when the Al composition ratio is 15% (0.15) or more, the influence of the off angle appears more. As a result, a surface having an off-angle outside the specified m-plane (for example, a surface having no off-angle in the a-axis direction, a surface having an off-angle in the c-axis direction larger than the off-angle in the a-axis direction, etc.) The effect of improving the surface with respect to the material using is increased, and the effect of improving the light emission efficiency is increased. In addition, when the Al composition ratio is 30% (0.30) or more, the influence of migration increases along with the influence of the off angle. For this reason, the improvement effect of the crystal quality with respect to another surface (for example, c surface) becomes large. In addition, a surface having an off-angle outside the specified range of the m-plane (for example, a surface having no off-angle in the a-axis direction or a surface having an off-angle in the c-axis direction larger than the off-angle in the a-axis direction). The effect of improving the surface with respect to the used one becomes larger, and the effect of improving the luminous efficiency becomes remarkable. Further, when the Al composition ratio is 50% (0.50) or more, the effect of improving the crystal quality with respect to other surfaces (for example, c-plane) becomes large. Furthermore, a surface having an off-angle outside the specified m-plane (for example, a surface having no off-angle in the a-axis direction or a surface having an off-angle in the c-axis direction larger than the off-angle in the a-axis direction). The surface improvement effect on the used one is further increased.

  Therefore, the effect of improving the crystal quality and flatness of the quantum well layer 120a can be increased by setting the Al composition ratio x1 of the quantum well layer 120a to 0.15 (15%) or more. If the Al composition ratio x1 of the quantum well layer 120a is 0.30 (30%) or more, the crystal quality and flatness improvement effect of the quantum well layer 120a can be further increased, and the Al composition ratio x1 Is 0.50 (50%) or more, the crystal quality and flatness improvement effect of the quantum well layer 120a can be further increased.

  In addition, by setting the Al composition ratio x1 of the quantum well layer 120a to 0.90 (90%) or less, the energy difference between the quantum well layer 120a and the barrier layer 120b and the energy difference between the carrier block layer 130 to some extent. Can be secured. Thereby, carrier confinement becomes possible.

  The barrier layer 120b has an Al composition ratio x2 that is greater than the Al composition ratio x1 of the quantum well layer 120a and is 0.20 (20%) or more and 1.00 (100%) or less. Since the band gap of the layer 120b is configured to be larger than the band gap of the quantum well layer 120a, carriers can be effectively confined in the quantum well. In addition, absorption of light from the active layer 120 can be suppressed. If the Al composition ratio x2 of the barrier layer 120b is 0.30 (30%) or more, the crystal quality and flatness of the barrier layer 120b can be further improved, and the Al composition ratio x1 is 0.50. If it is (50%) or more, the crystal quality and flatness of the barrier layer 120b can be further improved.

  The Al composition ratio x2 and the In composition ratio y2 of the barrier layer 120b are the layers adjacent to the barrier layer 120b in the n-side nitride semiconductor layer 210 formed between the barrier layer 120b and the nitride semiconductor layer 20. It is more preferable that the composition is the same as the composition. With this configuration, the lattice mismatch difference at the interface can be reduced.

  The layer structure 200 (nitride semiconductor layers, element structure) constituting the nitride semiconductor light emitting device 500 is formed by an epitaxial growth method such as metal organic chemical vapor deposition (MOCVD method) or molecular beam growth method (MBE method). Crystal growth method).

  Here, when an AlGaN layer or an AlN layer having a high Al composition ratio is formed, a growth temperature of 1200 ° C. or higher is used when the MOCVD method is used in order to improve the crystal quality by extending the migration of group III atoms. Often set to. However, in the temperature region exceeding 1200 ° C., the temperature load of the crystal growth apparatus (MOCVD apparatus) becomes large.

  In contrast, in the first embodiment, by configuring the growth surface 20a of the nitride semiconductor layer 20 as described above, the crystal quality can be improved even in a conventionally used temperature region. In addition, since appropriate migration can be controlled even in a temperature range lower than the conventionally used temperature range, the temperature can be lowered. For this reason, the temperature load applied to the crystal growth apparatus (MOCVD apparatus) can be reduced. In addition, growth in a temperature range where Ga evaporation can be suppressed is also possible. In addition, even when the growth is performed at a temperature lower than the conventionally used growth temperature (for example, about 1000 degrees), it is possible to suppress the deterioration of flatness.

  Further, if the quantum well layer 120a is composed of a nitride semiconductor layer containing In (for example, an AlInGaN layer), a layer having excellent flatness can be formed at a lower temperature. Therefore, considering the temperature load on the crystal growth apparatus, the quantum well layer 120a is preferably a nitride semiconductor layer containing Al and In (for example, an AlInGaN layer). In addition, since the quantum well layer 120a is composed of a nitride semiconductor layer containing Al and In (for example, an AlInGaN layer) as described above, one parameter for controlling strain is increased, thereby increasing the degree of freedom in design. You can also In addition, when the In composition ratio y is 12% (0.12) or less, a crystal having excellent flatness can be realized.

  On the other hand, the quantum well layer 120a may be formed of a nitride semiconductor layer (for example, an AlGaN layer) that does not contain In. If comprised in this way, the improvement effect of crystal quality and the improvement effect of flatness can be enlarged more. That is, when the nitride semiconductor layer 20 having the growth surface 20a is used, the effect of improving the crystal quality is obtained by growing a nitride semiconductor layer (for example, an AlGaN layer) not containing In on the growth surface 20a. In addition, the flatness improvement effect can be obtained more remarkably. In addition, it is preferable to configure the quantum well layer 120a from an AlGaN layer because an effect of reducing the operating voltage of the light emitting element can be obtained. In addition, the amount of In used can be reduced, which is preferable from the viewpoint of production cost.

Further, if the barrier layer 120b is composed of a nitride semiconductor layer containing In (for example, an AlInGaN layer), it is possible to form a layer having excellent flatness at a lower temperature like the quantum well layer 120a. Therefore, considering the temperature load on the crystal growth apparatus, the barrier layer 120b is preferably a nitride semiconductor layer containing Al and In (for example, an AlInGaN layer).
In addition, since the barrier layer 120b is composed of a nitride semiconductor layer containing Al and In (for example, an AlInGaN layer), the number of parameters for controlling strain is increased, thereby increasing the degree of freedom in design. You can also. In addition, the crystal | crystallization excellent in flatness is realizable by making In composition ratio y into 8% (0.80) or less.

  Further, the barrier layer 120b can be formed of a nitride semiconductor layer (for example, an AlGaN layer) that does not contain In. If comprised in this way, the improvement effect of crystal quality and the improvement effect of flatness can be enlarged more like the said quantum well layer 120a. Further, it is preferable that the barrier layer 120b as well as the quantum well layer 120a is made of an AlGaN layer because an effect of reducing the operating voltage of the light emitting element can be effectively obtained.

  Moreover, in 1st Embodiment, the fall of flatness can be suppressed by comprising so that the n side nitride semiconductor layer 210 may not contain a GaN layer. That is, a nitride semiconductor layer having a growth surface 20a having an off-angle in the a-axis direction and the c-axis direction with respect to the m-plane and the off-angle in the a-axis direction being larger than the off-angle in the c-axis direction When a GaN layer that is not intentionally doped with impurities or an n-type GaN layer doped with n-type impurities (for example, Si) is formed with a thickness of about 1.0 μm on 20, a phenomenon that the crystal surface becomes very rough is observed. Is done. On the other hand, in a p-type GaN layer intentionally doped with a p-type impurity (for example, Mg), a flat surface can be realized. This phenomenon is a phenomenon peculiar to the growth surface having the above configuration. For this reason, since the n-type GaN layer or the i-type GaN layer is configured not to be formed, it is possible to suppress the roughness of the crystal surface, and this can also improve the flatness. In addition, since the GaN layer absorbs light in the ultraviolet region, absorption of light emitted from the active layer 120 can be suppressed by configuring the GaN layer so as not to be provided.

  In addition, when a GaN substrate is used for the nitride semiconductor substrate 10, the GaN substrate absorbs ultraviolet light. Therefore, it is preferable to peel (remove) the GaN substrate using a general substrate peeling technique.

(Second Embodiment)
FIG. 7 is a cross-sectional view illustrating a nitride semiconductor light emitting device according to a second embodiment of the present invention. A nitride semiconductor light emitting device 600 according to the second embodiment of the present invention is now described with reference to FIGS. In FIG. 7, corresponding components are denoted by the same reference numerals, and redundant description is omitted as appropriate.

  As shown in FIG. 7, the nitride semiconductor light emitting device 600 of the second embodiment is configured as a so-called vertical structure light emitting diode device. Specifically, the n-side electrode 170 is formed on the back surface of the nitride semiconductor substrate 10, and the p-side electrode 160 is formed on the p-type contact layer 150.

  In the case of the vertical structure, since the template substrate 30 is composed of a conductive substrate, a conductive substrate such as a GaN substrate, an AlGaN substrate, or an AlInGaN substrate is used as the nitride semiconductor substrate 10 constituting the template substrate 30. Is preferred.

  When a GaN substrate is used as the nitride semiconductor substrate 10, the GaN substrate has conductivity unlike a sapphire substrate, so that the degree of freedom in device design is increased. In addition, compared to the case of using a different substrate such as a sapphire substrate, the difference in thermal expansion coefficient and lattice constant from the AlInGaN material is small, so that it is suitable for forming an AlInGaN layer. However, since the GaN substrate absorbs ultraviolet light, it needs to be designed in consideration of light absorption.

  When an AlGaN substrate is used as the nitride semiconductor substrate 10, the Al composition ratio of the AlGaN substrate is set higher than the Al composition ratio of the quantum well layer 120a (see FIG. 5), thereby suppressing the influence of light absorption. Unlike the case of using a GaN substrate, the design considering light absorption becomes unnecessary. For this reason, the design freedom of the element structure is increased. Furthermore, if the Al composition ratio of the AlGaN substrate is adjusted so that the lattice constant is close to that of the AlInGaN material constituting the light emitting element, a crack suppressing effect can also be expected. In this case, it is preferable that the multilayer constant (each nitride semiconductor layer) constituting the element structure be close to the lattice constant of the thickest layer.

  In addition, when an AlGaN substrate is used as the nitride semiconductor substrate 10, the degree of freedom of the lattice constant of the substrate is increased, so that the degree of freedom of design of the nitride semiconductor constituting the light emitting element is increased.

  When nitride semiconductor substrate 10 exhibits conductivity, nitride semiconductor layer 20 (nitride semiconductor layer 20 constituting template substrate 30) formed on growth surface 10a of nitride semiconductor substrate 10 is conductive. From this point of view, it may be made of AlGaN or AlInGaN. Since AlGaN and AlInGaN exhibit relatively good conductivity compared to AlN, electrodes are formed above and below the nitride semiconductor layer 200 (layer structure 200 (element structure)) to form a nitride semiconductor having a vertical structure. The light emitting element 600 can be realized.

  The layer structure 200 (nitride semiconductor layers 110 to 150 (nitride semiconductor layer 200)) formed on the template substrate 30 may be made of AlInGaN as in the first embodiment. Unlike the first embodiment, it may be made of AlGaN. Further, a configuration in which AlInGaN and AlGaN are mixed may be used. For example, when the active layer 120 is composed of an AlGaN layer, it is preferable that the n-side nitride semiconductor layer 210 and the p-side nitride semiconductor layer 220 sandwiching the active layer 120 are also composed of an AlGaN layer.

  It is also possible to use an AlN substrate for the nitride semiconductor substrate 10 or to configure the nitride semiconductor layer 20 from an AlN layer. In that case, if the AlN substrate or the AlN layer is peeled (removed), a nitride semiconductor light emitting element having a vertical structure can be manufactured.

  Other configurations and effects of the second embodiment are the same as those of the first embodiment.

(Third embodiment)
FIG. 8 is a sectional view showing a layer structure of a nitride semiconductor light emitting device according to the third embodiment of the present invention. Next, a nitride semiconductor light emitting device according to a third embodiment of the present invention will be described with reference to FIG.

  In the nitride semiconductor light emitting device according to the third embodiment, the nitride semiconductor layer 20 constituting the template substrate 30 is composed of a GaN layer 21 as shown in FIG. In the third embodiment, the GaN layer 21 (nitride semiconductor layer 20) has a thickness of 0.7 μm or less. The thickness of the GaN layer 21 (nitride semiconductor layer 20) is more preferably 0.5 μm or less, and even more preferably 0.2 μm or less.

  As described above, with respect to the m-plane, a nitride having an off-angle in the a-axis direction and the c-axis direction, and a growth surface having a plane in which the off-angle in the a-axis direction is larger than the off-angle in the c-axis direction When a GaN layer not intentionally doped with impurities or an n-type GaN layer doped with n-type impurities (for example, Si) is formed on a semiconductor layer (nitride semiconductor substrate) to a thickness of about 1.0 μm, the crystal surface A very rough phenomenon is observed. On the other hand, in a p-type GaN layer intentionally doped with a p-type impurity (for example, Mg), a flat surface can be realized. This phenomenon is a phenomenon peculiar to the growth surface having the above configuration. Therefore, when a GaN layer having a thickness of about 1.0 μm is formed as the nitride semiconductor layer 20 on the growth surface 10 a of the nitride semiconductor substrate 10, the crystal surface may be roughened.

  On the other hand, even when a GaN layer is formed as the nitride semiconductor layer 20 on the growth surface 10a of the nitride semiconductor substrate 10, the influence (surface roughness) due to the off angle can be reduced by reducing the thickness. It becomes possible. In this case, if the thickness of the GaN layer 21 (nitride semiconductor layer 20) is 0.5 μm or less, the influence can be further reduced. If the thickness of the GaN layer 21 (nitride semiconductor layer 20) is 0.2 μm or less, the influence can be further reduced.

  The element structure (nitride semiconductor layers 110 to 150 (nitride semiconductor layer 200)) formed on the growth surface 20a of the template substrate 30 is the same as in the first and second embodiments. In addition, the nitride semiconductor light emitting device according to the third embodiment may have either a vertical structure or a horizontal structure. At that time, the n-side electrode and the p-side electrode can have the same configuration as the electrodes shown in the first and second embodiments.

  The effects of the third embodiment are the same as those of the first and second embodiments.

(Fourth embodiment)
FIG. 9 is a cross-sectional view illustrating a nitride semiconductor light emitting device according to a fourth embodiment of the present invention. FIG. 10 is a cross-sectional view of a template substrate used in the nitride semiconductor light emitting device according to the fourth embodiment of the present invention. Next, a nitride semiconductor light emitting device 700 according to a fourth embodiment of the present invention will be described with reference to FIGS. In addition, in each figure, the same code | symbol is attached | subjected to a corresponding component, and the overlapping description is abbreviate | omitted suitably.

  In the fourth embodiment, as shown in FIGS. 9 and 10, the base substrate 710 constituting the template substrate 30 is composed of a substrate other than the nitride semiconductor substrate. Specifically, in the fourth embodiment, the base substrate 710 is composed of, for example, a sapphire substrate, a SiC substrate, a Si substrate, or the like.

  A first nitride semiconductor layer 720 is formed on the growth surface 710 a of the base substrate 710. The first nitride semiconductor layer 720 is composed of, for example, an AlN layer, an AlGaN layer, an AlInGaN layer, or the like. The first nitride semiconductor layer 720 is more preferably composed of an AlN layer. Further, the growth surface 720a of the first nitride semiconductor layer 720 has off-angles in the a-axis direction and the c-axis direction with respect to the m-plane, as in the first to third embodiments, and the a-axis direction. Is formed of a surface whose off angle is larger than the off angle in the c-axis direction. In addition, it is more preferable if the off angle in the a-axis direction is configured to be greater than 0.1 degrees and 10 degrees or less. More preferably, the angle is greater than 1.0 degree and 10 degrees or less.

  In the fourth embodiment, the second nitride semiconductor layer 730 is further formed on the growth surface 720 a of the first nitride semiconductor layer 720. The second nitride semiconductor layer 730 is composed of, for example, an AlN layer, an AlGaN layer, an AlInGaN layer, or the like. Each of the first nitride semiconductor layer 720 and the second nitride semiconductor layer 730 is an example of the “semiconductor layer having a growth surface” in the present invention.

  Nitride semiconductor formed on growth surface 720a having an off-angle in the a-axis direction and the c-axis direction with respect to the m-plane and having an off-angle in the a-axis direction larger than the off-angle in the c-axis direction The higher the Al composition ratio of the layer (second nitride semiconductor layer 730), the greater the effect of improving crystallinity and flatness with respect to other surfaces. For this reason, the improvement effect of crystal quality and flatness becomes large by making the 2nd nitride semiconductor layer 730 into an AlN layer.

  Further, the growth surface 730a of the second nitride semiconductor layer 730 formed on the growth surface 720a of the first nitride semiconductor layer 720 is also in the a-axis direction and the c-axis direction with respect to the m-plane, like the growth surface 720a. The surface has an off angle and the off angle in the a-axis direction is larger than the off angle in the c-axis direction.

  Further, on the growth surface 730 a of the template substrate 30, the same element structure (nitride semiconductor layers 110 to 150 (nitride semiconductor layer 200)) as in the first to third embodiments is formed. Each of the nitride semiconductor layers 110 to 150 may be made of AlInGaN or AlGaN.

  In the fourth embodiment, as described above, the growth surface 730a of the nitride semiconductor template formed on the base substrate 710 such as the sapphire substrate, the SiC substrate, or the Si substrate is set to the a-axis direction and the c-axis with respect to the m-plane. The crystal quality of each of the nitride semiconductor layers 110 to 150 formed on the growth surface 730a is such that the off-angle in the direction and the off-angle in the a-axis direction are larger than the off-angle in the c-axis direction. Further, the flatness can be improved. For this reason, when the nitride semiconductor light emitting device is manufactured, the light emission efficiency can be improved.

  Note that the template substrate 30 in the fourth embodiment may be configured without the second nitride semiconductor layer 730.

  Further, when a sapphire substrate is used as the base substrate 710, the nitride semiconductor light emitting device 700 can have a lateral structure as shown in FIG. Further, when at least one of the first nitride semiconductor layer 720 and the second nitride semiconductor layer 730 is composed of an AlN layer, the AlN layer is inferior in conductivity as compared to an AlGaN layer, an AlInGaN layer, or the like. As shown in FIG. 4, the nitride semiconductor light emitting device 700 is preferably a lateral structure.

  On the other hand, when the template substrate 30 has conductivity, the nitride semiconductor light emitting device 700 can have a vertical structure.

  Other configurations and effects of the fourth embodiment are the same as those of the first and second embodiments.

(Fifth embodiment)
FIG. 11 is a cross-sectional view illustrating a nitride semiconductor light emitting device according to a fifth embodiment of the present invention. Next, a nitride semiconductor light emitting device 800 according to a fifth embodiment of the present invention will be described with reference to FIG. Note that, in FIG. 11, corresponding components are denoted by the same reference numerals, and redundant description is omitted as appropriate.

  In the fifth embodiment, as shown in FIG. 11, the layer structure 200 (the nitride semiconductor layers 110 to 150) is formed directly on the growth surface 10 a of the nitride semiconductor substrate 10. The nitride semiconductor substrate 10 is composed of, for example, a GaN substrate, an AlGaN substrate, an AlInGaN substrate, an AlN substrate, or the like. The growth surface 10a has off-angles in the a-axis direction and the c-axis direction with respect to the m-plane, and the off-angle in the a-axis direction is the c-axis direction, as in the first to fourth embodiments. The surface is larger than the off angle. It is more preferable that the off angle in the a-axis direction is configured to be greater than 0.1 degree and 10 degrees or less. More preferably, the angle is greater than 1.0 degree and 10 degrees or less. The nitride semiconductor substrate 10 in the fifth embodiment is an example of the “semiconductor layer having a growth surface” in the present invention.

  Further, on the growth surface 10 a of the nitride semiconductor substrate 10, the same element structure (nitride semiconductor layers 110 to 150) as in the first to fourth embodiments is formed. When nitride semiconductor substrate 10 is made of a conductive substrate, nitride semiconductor light emitting element 800 can have a vertical structure as shown in FIG. Further, when the nitride semiconductor substrate 10 is composed of an AlN substrate, the AlN substrate is inferior in conductivity compared to a GaN substrate, an AlGaN substrate, an AlInGaN substrate, etc. Good.

  In the fifth embodiment, as described above, the growth surface 10a of the nitride semiconductor substrate 10 has off-angles in the a-axis direction and the c-axis direction with respect to the m-plane, and the off-angle in the a-axis direction is By making the surface larger than the off-angle in the c-axis direction, the crystal quality and flatness of the nitride semiconductor layers 110 to 150 formed on the growth surface 10a can be improved. For this reason, when the nitride semiconductor light emitting device 800 is manufactured, the light emission efficiency can be improved.

  Other configurations and effects of the fifth embodiment are the same as those of the first and second embodiments.

(Sixth embodiment)
FIG. 12 is a cross-sectional view illustrating a nitride semiconductor light emitting device according to a sixth embodiment of the present invention. Next, a nitride semiconductor light emitting device 900 (900A) according to the sixth embodiment of the present invention will be described with reference to FIG. In FIG. 12, corresponding components are denoted by the same reference numerals, and redundant description will be omitted as appropriate.

  In the sixth embodiment, in the configuration of the fifth embodiment, an AlN layer 910 is formed on the growth surface 10a of the nitride semiconductor substrate 10 so as to be in contact with the growth surface 10a. That is, in the sixth embodiment, in the configuration of the fifth embodiment, an AlN layer 910 is formed between the nitride semiconductor substrate 10 and the element structure (nitride semiconductor layer 200).

  Thus, by forming the AlN layer 910 on the growth surface 10a of the nitride semiconductor substrate 10, the crystallinity is greatly improved compared to the AlN layer formed on the other surface (for example, the c-plane). In addition, on a surface having an off-angle outside the specification of the m-plane (for example, a surface having no off-angle in the a-axis direction or a surface having an off-angle in the c-axis direction larger than the off-angle in the a-axis direction). Compared with the formed AlN layer, the flatness is greatly improved. Therefore, by forming an element structure (layer structure 200 (nitride semiconductor layers 110 to 150)) on this AlN layer 910, the formation quality of the element structure (layer structure 200 (nitride semiconductor layers 110 to 150)) is formed. In addition, the flatness can be further improved.

  Therefore, with this configuration, nitride semiconductor light emitting device 900 (900A) with improved luminous efficiency can be obtained.

  Since the AlN layer 910 is inferior in conductivity as compared with an AlGaN layer, an AlInGaN layer, a GaN layer, or the like, the nitride semiconductor light-emitting element may have a lateral structure as shown in FIG. Further, if the AlN layer 910 is also peeled off (removed) together with the substrate, it is possible to realize a nitride semiconductor light emitting element having a vertical structure. In that case, the n-side nitride semiconductor layer 210 constituting the element structure is an example of the “semiconductor element having a growth surface” in the present invention.

  Other configurations and effects of the sixth embodiment are the same as those of the fifth embodiment.

(Modification of the sixth embodiment)
FIG. 13 is a cross-sectional view showing a nitride semiconductor light emitting device according to a modification of the sixth embodiment. Referring to FIG. 13, in a nitride semiconductor light emitting device 900 (900B) according to a modification of the sixth embodiment, an AlN layer 910 is formed on the growth surface of the template substrate 30 shown in the first to fourth embodiments. It has a formed configuration. That is, in the sixth embodiment, the configuration in which the AlN layer 910 is formed directly on the growth surface 10a of the nitride semiconductor substrate 10 is shown. However, in the modification of the sixth embodiment, the template substrate 30 An AlN layer 910 is directly formed on the growth surface.

  Other configurations in the modified example of the sixth embodiment are the same as those in the sixth embodiment.

  FIG. 14 is a cross-sectional view showing the nitride semiconductor light emitting device according to Example 1. FIG. 15 is a cross-sectional view showing the configuration of the active layer of the nitride semiconductor light emitting device according to Example 1. A nitride semiconductor light emitting device 850 according to Example 1 will be described with reference to FIGS.

In Example 1, as shown in FIG. 14, an n-type Al _0.45 Ga _0.55 N layer 110 having a thickness of about 0.1 μm was formed on the growth surface 10 a of the nitride semiconductor substrate 10. An active layer 120 was formed on the n-type Al _0.45 Ga _0.55 N layer 100. On the active layer 120, a carrier block layer 130 made of p-type Al _0.75 Ga _0.25 N having a thickness of about 15 nm, and a p-type Al _0.60 Ga _0.40 N layer 140 having a thickness of about 20 nm. A p-type GaN layer 150 having a thickness of about 50 nm was sequentially formed.

Further, as shown in FIG. 15, the active layer 120 is configured in a quantum well structure by alternately stacking barrier layers 120 b and quantum well layers 120 a. The number of quantum well layers 120a was two. In Example 2, the quantum well layer 120a was Al _0.36 Ga _0.64 N, and the barrier layer 120b was Al _0.45 Ga _0.55 N. In Example 1, a GaN substrate was used as the nitride semiconductor substrate 10.

  In Example 1, the nitride semiconductor light emitting device 850 was configured in a lateral structure by forming two electrodes (p-side electrode 160 and n-side electrode 170) on the upper surface side of the nitride semiconductor substrate 10. The p-side electrode 160 and the n-side electrode 170 are the same as in the above embodiment. However, in Example 1, the nitride semiconductor light emitting device 850 can be configured in a vertical structure by forming electrodes on the upper surface side and the lower surface side of the nitride semiconductor substrate 10.

  Next, using a GaN substrate (substrate 1) having an off angle in the a-axis direction of 1 degree or less and a GaN substrate (substrate 2) greater than 1 degree, the same nitride semiconductor light-emitting element as in Example 1 above Was made. The specific off-angle of the substrate 1 is 0.8 degrees in the a-axis direction and the off-angle in the c-axis direction is −0.5 degrees, and the specific off-angle of the substrate 2 is in the a-axis direction. The off angle was 1.85 degrees, and the off angle in the c-axis direction was −0.2 degrees. Then, using these elements, the light emission intensity by operating voltage and current injection was compared.

  As a result, an element using a GaN substrate (substrate 2) having an off angle in the a-axis direction larger than 1 degree, and an element using a GaN substrate (substrate 1) having an off angle in the a-axis direction of 1 degree or less. The operating voltage was reduced by about 0.8V. Further, when the light emission intensity by current injection was compared, the light emission intensity of the element using the substrate 2 was able to obtain light emission about three times stronger than the light emission intensity of the element using the substrate 1. This is considered to be because the flatness was further improved by setting the off angle in the a-axis direction to be larger than 1 degree. It is considered that the light emission intensity is increased due to the effect of suppressing the light emission other than the predetermined light emission wavelength caused by the fluctuation of the layer thickness and the effect of uniform current injection, etc. by improving the flatness. .

  FIG. 16 is a cross-sectional view showing a nitride semiconductor light emitting device according to Example 2. FIG. 17 is a cross-sectional view showing the configuration of the active layer of the nitride semiconductor light emitting device according to Example 2. A nitride semiconductor light emitting device 860 according to Example 2 will be described with reference to FIGS. 16 and 17.

In Example 2, an n-type Al _0.50 Ga _0.50 N layer 110 having a thickness of about 0.1 μm was formed on the growth surface 10a of the nitride semiconductor substrate 10 as shown in FIG. On the n-type Al _0.50 Ga _0.50 N layer 110, the active layer 120, a carrier block layer 130 made of p-type Al _0.80 Ga _0.20 N having a thickness of about 15 nm, A p-type contact layer 150 made of p-type Al _0.50 Ga _0.50 N layer 140 having a thickness and p-type Al _0.10 Ga _0.90 N having a thickness of about 50 nm was sequentially formed.

Further, as shown in FIG. 17, the active layer 120 is configured in a quantum well structure by alternately stacking barrier layers 120 b and quantum well layers 120 a. The number of quantum well layers 120a was five. In Example 2, the quantum well layer 120a was Al _0.4 Ga _0.6 N, and the barrier layer 120b was Al _0.50 Ga _0.50 N. In Example 2, a GaN substrate was used as the nitride semiconductor substrate 10.

  In the second embodiment, as in the first embodiment, two electrodes (p-side electrode 160 and n-side electrode 170) are formed on the upper surface side of the nitride semiconductor substrate 10, so that the nitride semiconductor light-emitting element 860 is formed in a horizontal type. Configured to structure. The p-side electrode 160 and the n-side electrode 170 are the same as in the above embodiment. However, also in Example 2, the nitride semiconductor light emitting device 860 can be configured in a vertical structure by forming electrodes on the upper surface side and the lower surface side of the nitride semiconductor substrate 10.

  18 is a cross-sectional view of an evaluation structure used for confirming the effect of improving the light emission efficiency of the nitride semiconductor light emitting device according to Example 2. FIG.

As shown in FIG. 18, this evaluation structure (Example 2) is shown in FIG. 16 up to the nitride semiconductor substrate 10, the n-type Al _0.50 Ga _0.50 N layer 110, and the active layer 120. The semiconductor layer formed on the active layer 120 is the same as the configuration of the second embodiment, and is different from the configuration of the second embodiment. Specifically, in this evaluation structure, instead of the carrier block layer 130, the p-type Al _0.50 Ga _0.50 N layer 140, and the p-type contact layer 150, the active layer 120 has a thickness of about 20 nm. An AlN cap layer 810 was formed. The off-angle of the nitride semiconductor substrate (GaN substrate) 10 is 2.05 degrees in the a-axis direction and −0.15 degrees in the c-axis direction. In addition, this evaluation structure is composed only of a semiconductor layer structure, with no n-side electrode and p-side electrode formed. Then, PL (photoluminescence) intensity was measured using this evaluation structure.

  As a comparative evaluation structure, the off-angle in the c-axis direction is larger than the off-angle in the a-axis direction with the sample (Comparative Example 1) in which the same layer structure is formed on the GaN substrate having the c-plane as the growth surface. A sample (Comparative Example 2) in which a similar layer structure was formed on a GaN substrate having a surface as a growth surface was produced. The specific off-angle of Comparative Example 2 is 0.08 degrees in the a-axis direction and -1.2 degrees in the c-axis direction. And about these samples (comparative example 1, comparative example 2), PL intensity | strength was measured similarly and the comparison with Example 2 was performed.

  As a result, the evaluation structure (Example 2 and Comparative Example 2) using the GaN substrate whose growth surface is a surface having an off angle with respect to the m-plane is the same layer on the GaN substrate whose growth surface is the c-plane. It was confirmed that the PL intensity was three times or more stronger than the evaluation structure (Comparative Example 2) in which the structure was formed. This is presumed to be due to the fact that the group III atom migration has been extended, thereby improving the crystal quality. Another reason is considered to be the effect of suppressing the influence of spontaneous polarization.

  When the evaluation structures (Example 2 and Comparative Example 2) using GaN substrates having a growth surface with an off-angle with respect to the m-plane are compared, the evaluation structure of Example 2 is the evaluation structure of Comparative Example 2. As a result, the PL intensity was about twice as strong. In the evaluation structure of Example 2, it is considered that the light emission intensity is increased because the flatness is improved and the light emission other than the predetermined light emission wavelength caused by the layer thickness fluctuation is suppressed. .

  From the above results, it was confirmed that the effect of improving the crystal quality and flatness is increased by making the off angle in the a-axis direction larger than the off-angle in the c-axis direction.

(Seventh embodiment)
FIG. 19 is a cross-sectional view illustrating a semiconductor substrate according to a seventh embodiment of the present invention. Next, with reference to FIG. 19, in the seventh embodiment, a semiconductor substrate used for a nitride semiconductor light emitting device will be described.

  As shown in FIG. 19, the semiconductor substrate 300 according to the seventh embodiment includes a base substrate 310 and a nitride semiconductor layer 320 formed on the growth surface 310 a of the base substrate 310. The nitride semiconductor layer 320 constituting the semiconductor substrate 300 has a growth surface 320a composed of surfaces having off-angles in the a-axis direction and the c-axis direction with respect to the m-plane. In the growth surface 320a, the off angle in the a-axis direction is larger than the off angle in the c-axis direction. Further, the off angle in the a-axis direction is set to be greater than 0.1 degree and 10 degrees or less. The off angle in the a-axis direction is more preferably greater than 1 degree and less than 10 degrees. The nitride semiconductor layer 320 is an example of the “semiconductor layer having a growth surface” in the present invention.

Also, for example, a nitride semiconductor layer 400 containing Al is formed on the growth surface 320a of the semiconductor substrate 300 (nitride semiconductor layer 320). Specifically, in the seventh embodiment, a nitride semiconductor layer made of Al _x In _y Ga _1-xy N having a thickness of about 1.0 μm on the growth surface 320 a of the nitride semiconductor layer 320. 400 is formed.

  As the base substrate 310, for example, a GaN substrate, AlGaN substrate, AlInGaN substrate, AlN substrate, sapphire substrate, SiC substrate, Si substrate, or the like can be used. For the nitride semiconductor layer 320, for example, a GaN layer, an AlGaN layer, an AlInGaN layer, an AlN layer, or the like can be used.

  Further, as described above, when the nitride semiconductor layer 400 containing Al is formed on the nitride semiconductor layer 320 having the growth surface 320a, as the Al composition ratio increases, at least a with respect to the m-plane. When a growth surface having an off angle in the axial direction and having an off angle in the a-axis direction larger than the off-angle in the c-axis direction is used, a surface other than the above surfaces (for example, The effect of improving the crystal quality of the material using the c-plane) is increased. In addition, a surface having an off-angle outside the specified range of the m-plane (for example, a surface having no off-angle in the a-axis direction or a surface having an off-angle in the c-axis direction larger than the off-angle in the a-axis direction). The improvement effect of the flatness with respect to what was used becomes large. When a specific nitride semiconductor light emitting device is formed, the Al composition ratio x of the nitride semiconductor layer 400 formed on the growth surface 320a is in the range of 0.15 ≦ x ≦ 1.00. Preferably, it is more preferable if it is in the range of 0.30 ≦ x ≦ 1.00. The In composition ratio y is preferably in the range of 0.00 ≦ y ≦ 0.12.

  When the Al composition ratio x is set to 15% (0.15) or more, the influence of the off angle appears more. Therefore, a surface having an off angle outside the specified range of the m plane (for example, having an off angle in the a-axis direction). Surface improvement effect for a surface using a non-moving surface or a surface using an off-angle in the c-axis direction larger than the off-angle in the a-axis direction. In addition, by setting the Al composition ratio x to be 30% (0.30) or more, the influence of migration is increased along with the influence of the off angle, so that the effect is increased, and the other surface (for example, c-plane) is affected. The crystal quality improvement effect is further increased. In addition, a surface having an off-angle outside the specified range of the m-plane (for example, a surface having no off-angle in the a-axis direction, a surface having an off-angle in the c-axis direction larger than the off-angle in the a-axis direction, etc.) The flatness with respect to the material using is improved. It is preferable that the Al composition ratio x is 50% (0.50) or more because the effect of improving other surfaces (for example, the c-plane) is increased.

  Then, by using the semiconductor substrate 300 configured in this way, it is possible to improve the crystal quality and flatness of the nitride semiconductor layer containing Al formed on the growth surface 320a. This is also confirmed from the measurement result of PL (photoluminescence) characteristics. Specifically, a sample in which the nitride semiconductor layer 400 is formed on the growth surface 320a of the nitride semiconductor layer 320 (for example, an AlGaN layer) according to the seventh embodiment, and a nitride semiconductor having the c-plane as the growth surface. A sample in which a semiconductor layer similar to the nitride semiconductor layer 400 was formed on a layer (for example, an AlGaN layer) and PL characteristics were compared. As a result, the nitride semiconductor layer 320 according to the seventh embodiment ( With the sample using the semiconductor substrate 300), the result that the luminous efficiency was improved was obtained. Thus, the light emission efficiency can be improved by using the nitride semiconductor layer 320 (semiconductor substrate 300) according to the seventh embodiment. This is presumably because the surface migration of group III atoms reaching the substrate surface (growth surface 320a of the nitride semiconductor layer 320) has been extended.

  In the seventh embodiment, by using such a semiconductor substrate 300, when the nitride semiconductor layer 400 is formed on the growth surface 320a, the growth temperature is set to a temperature load for the crystal growth apparatus (MOCVD apparatus). Even if the temperature is not set to a high temperature (for example, 1200 ° C. or higher), the crystal quality can be improved. For this reason, by using such a semiconductor substrate 300, the temperature load applied to the crystal growth apparatus (MOCVD apparatus) can be reduced. In addition, even when the growth is performed at a temperature lower than the conventionally used growth temperature (for example, about 1000 degrees), it is possible to suppress the deterioration of flatness.

  Furthermore, by using the nitride semiconductor layer 400 formed on the growth surface 320a as a nitride semiconductor layer containing In (for example, an AlInGaN layer), a layer having excellent flatness can be formed at a lower temperature. It becomes. Therefore, considering the temperature load on the crystal growth apparatus, the nitride semiconductor layer 400 formed on the growth surface 320a is preferably a nitride semiconductor layer containing Al and In. Further, as described above, when the nitride semiconductor layer 400 is composed of a nitride semiconductor layer containing Al and In (for example, an AlInGaN layer), strain is formed when an element structure is formed on the growth surface 320a. Since the number of parameters for controlling is increased by one, the degree of freedom in design can be increased. In addition, the crystal | crystallization excellent in flatness is realizable by making In composition ratio y into 12% (0.12) or less.

  On the other hand, the nitride semiconductor layer 400 formed on the growth surface 320a may be a nitride semiconductor layer that does not contain In (for example, an AlGaN layer). If comprised in this way, the improvement effect of crystal quality and the improvement effect of flatness can be enlarged more. That is, when the nitride semiconductor layer 400 having the growth surface 320a is used, an effect of improving crystal quality can be obtained by growing a nitride semiconductor layer (for example, an AlGaN layer) not containing In on the growth surface 320a. In addition, the flatness improvement effect can be obtained more remarkably.

  In addition, by setting the off angle in the a-axis direction on the growth surface 320a to be greater than 0.1 degree and 10 degrees or less, generation of pyramid-shaped convex portions can be suppressed, so that flatness is improved. be able to. Moreover, since a favorable surface morphology can be obtained, variations in layer thickness can be suppressed. Thereby, generation | occurrence | production of a crack can be suppressed, and the improvement of luminous efficiency and reduction of element resistance can be implement | achieved. Further, by setting the off angle in the a-axis direction to be greater than 1 degree and 10 degrees or less, a greater effect can be obtained.

  The nitride semiconductor layer 400 formed on the growth surface 320a can also be an AlN layer.

  Thus, the semiconductor substrate 300 according to the seventh embodiment can improve the crystallinity and flatness of the nitride semiconductor layer 400 containing Al formed on the growth surface 320a. Therefore, if a specific element structure is formed using such a semiconductor substrate 300, a nitride semiconductor light emitting element with high luminous efficiency can be formed.

  Such a semiconductor substrate 300 is very useful as a seed substrate for forming a nitride semiconductor substrate. For example, by using the nitride semiconductor layer 320 of the semiconductor substrate 300 as a seed layer, the nitride semiconductor layer 400 containing Al is formed on the growth surface 320a so as to have a thickness (for example, about 350 μm) that allows the AlGaN substrate to stand by itself. A nitride semiconductor substrate such as an AlInGaN substrate or an AlN substrate can be obtained. In this case, it is preferable that the nitride semiconductor layer 320 to be a seed layer and the nitride semiconductor layer 400 formed on the growth surface 320a have the same composition. At that time, the semiconductor substrate 300 may be peeled off by polishing, etching, laser lift-off, or the like, or may be left without being peeled off. Further, only the base substrate 310 of the semiconductor substrate 300 may be peeled off.

  Furthermore, the semiconductor substrate 300 in which the nitride semiconductor layer 400 is formed can be used as the substrate. For example, an AlN layer can be formed on the growth surface 320a of the nitride semiconductor layer 320 in the semiconductor substrate 300, and an element structure can be formed on the main surface of the AlN layer. Similarly to the growth surface 320a, the main surface of the AlN layer formed on the growth surface 320a also has off-angles in the a-axis direction and the c-axis direction with respect to the m-plane, and the off-angle in the a-axis direction is c The surface is configured to be larger than the axial off-angle. For this reason, also in the nitride semiconductor layer containing Al formed on the main surface of the AlN layer, crystal quality and flatness can be improved. Therefore, when a light emitting element is formed using such a substrate, the light emission efficiency can be improved and the operating voltage can be reduced.

  Further, the semiconductor substrate 300 is composed only of a nitride semiconductor substrate (for example, a GaN substrate, an AlGaN substrate, an AlInGaN substrate, an AlN substrate) having a growth surface similar to the growth surface 320a of the nitride semiconductor layer 320. May be.

  Note that when the base substrate 310 of the semiconductor substrate 300 is a GaN substrate, it has conductivity, unlike a sapphire substrate, so that the degree of freedom in device design can be increased. In addition, since a difference in thermal expansion coefficient and a difference in lattice constant from AlInGaN is small compared to the case of using a dissimilar substrate such as a sapphire substrate, an AlInGaN layer with good crystallinity can be formed.

  In addition, when the base substrate 310 of the semiconductor substrate 300 is an AlGaN substrate, absorption of light with respect to ultraviolet light can be suppressed. Further, when the base substrate 310 of the semiconductor substrate 300 is an AlInGaN substrate, the degree of freedom of the lattice constant is increased, so that the degree of freedom in designing the layer structure constituting the device can be increased. Further, when the base substrate 310 of the semiconductor substrate 300 is an AlN substrate, in addition to the same effect as the AlGaN substrate, heat dissipation can be improved.

  Further, the base substrate 310 of the semiconductor substrate 300 may be a substrate other than a nitride semiconductor substrate such as a sapphire substrate, a SiC substrate, or a Si substrate. Even in this case, by configuring the growth surface 320a of the nitride semiconductor layer 320 formed on the base substrate 310 as described above, an effect of improving the crystal quality and an effect of improving the flatness can be obtained. In this case, as shown in the fourth embodiment, a plurality of nitride semiconductor layers may be stacked on the base substrate 310.

  In Example 3, a GaN substrate was used as an example of a semiconductor substrate, and an AlGaN layer having a thickness of about 0.1 μm was formed on the growth surface. As for the off-angle of the growth surface, the off-angle in the a-axis direction was -1.99 degrees, and the off-angle in the c-axis direction was -0.20 degrees. Further, samples having Al composition ratios of the AlGaN layer of 5%, 10%, 18%, and 35% were prepared, and the PL intensity was measured.

  As a comparative sample 1, a sample in which a similar AlGaN layer was formed on a GaN substrate having a c-plane as a growth surface was prepared. Further, as a comparative sample 2, a sample in which a similar AlGaN layer was formed on a GaN substrate having a growth surface with a surface having a larger off angle in the c-axis direction than the off angle in the a-axis direction was produced. Specifically, the off angle in the a-axis direction is −0.07 degrees, and the off angle in the c-axis direction is −0.35 degrees. For these samples, the PL intensity was similarly measured and compared with Example 3.

  A sample using a GaN substrate having a growth surface with an off-angle with respect to the m-plane (Example 3, comparative sample 2) has a c-plane when the Al composition ratio of the AlGaN layer is 5% to 10%. Although the PL intensity was almost the same as that of the sample using the GaN substrate as the growth surface (Comparative Sample 1), the PL intensity was increased as compared with Comparative Sample 1 when the Al composition ratio was 18% to 35%. . Further, the rate of increase in PL intensity with respect to the comparative sample 1 was about twice as large in the case of 35% as compared with the case where the Al composition ratio was 18%. From this, it is speculated that the higher the Al composition ratio, the greater the influence of Al migration, and the more effective the effect of extending the migration in a GaN substrate whose growth surface is a surface having an off angle with respect to the m-plane. Is done.

  When samples using GaN substrates (Example 3, Comparative Sample 2) having a growth surface with an off-angle with respect to the m-plane are compared, the Al composition ratio of the AlGaN layer is 5% to 10%. Then, almost the same PL strength was obtained, but when the Al composition ratio was 18% and 35%, the PL strength was about 1.5 times stronger in Example 3 than in Comparative Sample 2. . Further, in Example 3, the flatness of the layer surface was better than that of Comparative Sample 2. Moreover, the influence was remarkable at 18% and 35% with high Al composition ratio. And, it is considered that the emission intensity is increased because the improvement in flatness suppresses the light emission other than the predetermined light emission wavelength caused by the layer thickness fluctuation.

  From the above results, it was confirmed that the effect of improving the crystal quality and flatness is increased by making the off angle in the a-axis direction larger than the off-angle in the c-axis direction.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and further includes all modifications within the meaning and scope equivalent to the scope of claims for patent.

  For example, in the first to seventh embodiments, the example in which each nitride semiconductor layer is crystal-grown on the substrate by using the MOCVD method has been shown. However, the present invention is not limited to this, but other than the MOCVD method. A crystal growth method may be used to grow each nitride semiconductor layer on a substrate. For example, each nitride semiconductor layer may be crystal-grown using an MBE method (Molecular Beam Epitaxy), an HDVPE method (Hydride Vapor Phase Epitaxy), or the like.

  Moreover, in the said 1st-7th embodiment, the growth surface of the nitride semiconductor layer (nitride semiconductor substrate) was comprised from the surface which has an off angle in both a-axis direction and c-axis direction with respect to m surface. However, the present invention is not limited to this, and the growth surface of the nitride semiconductor layer (nitride semiconductor substrate) may be formed from a surface having an off angle at least in the a-axis direction with respect to the m-plane. Good. That is, the off angle in the c-axis direction may be 0 degrees.

  Moreover, although the example which applied this invention to the light emitting diode element which is an example of the nitride semiconductor element was shown in the said 1st-6th embodiment, this invention is not limited to this, Nitride other than a light emitting diode element The present invention can also be applied to semiconductor light emitting devices. For example, the present invention can be applied to a nitride semiconductor laser element which is an example of a nitride semiconductor light emitting element. When a GaN substrate is used as the substrate, the GaN substrate absorbs ultraviolet light, so that, for example, a multilayer reflector is formed between the substrate and the active layer in order to reduce light leakage to the substrate. Is preferred. Further, when light extraction on the substrate side is performed in application to a light emitting diode element, it is preferable to peel off the GaN substrate or to remove the light extraction portion on the GaN substrate by etching or the like. In this way, light extraction on the substrate side can be facilitated. Further, when light is extracted from the side opposite to the substrate with respect to the active layer, if a GaN layer (p-type GaN layer) is formed as a contact layer, light absorption occurs in the GaN layer. It is preferable to adopt a configuration in which the is removed by etching or the like.

  The present invention is not limited to nitride semiconductor light emitting elements such as light emitting diode elements and semiconductor laser elements, but also devices using nitride semiconductors such as electronic devices (for example, power transistors, integrated circuits (ICs), LSIs (Large). Scale integration), etc.).

  In the above embodiment, the nitride semiconductor layer having the growth surface is formed by growing on the substrate. Here, “growing on the substrate” means directly growing on the growth surface of the substrate. And a case where a nitride semiconductor having a growth surface is formed on a substrate and a nitride semiconductor layer is formed thereon. The growth surface of the nitride semiconductor layer is not limited to the main surface, and a facet generated when lateral growth is performed using a mask or the like can be used as the growth surface. That is, the above “grow on the substrate” includes the case where the nitride semiconductor layer is grown on such a growth surface.

  In the above-described embodiment, the element structure (nitride semiconductor layers) formed on the growth surface of the nitride semiconductor layer is appropriately combined or changed in thickness, composition, etc., to suit the desired characteristics. It is possible to For example, the semiconductor layers may be added or deleted, or the order of the semiconductor layers may be partially changed. Further, for example, even if a semiconductor layer having a superlattice structure is formed between the nitride semiconductor layer 20 and the n-type nitride semiconductor layer 110 (for example, an n-type AlInGaN layer or an n-type AlGaN layer) in FIG. Good. In this case, it is preferable to form a superlattice structure on the growth surface of the nitride semiconductor layer because a superlattice structure having excellent flatness can be formed. Furthermore, the conductivity type may be changed for some semiconductor layers. That is, it can be freely changed as long as basic characteristics as a nitride semiconductor element (including a nitride semiconductor laser element and a light emitting diode element) are obtained.

  In addition, when the difference between the lattice constant of the nitride semiconductor layer stacked on the substrate and the lattice constant of the substrate is large, a crack may occur in the stacked nitride semiconductor layer. In this case, it is possible to suppress the occurrence of cracks by forming grooves (concave portions) in the substrate.

  Moreover, although the said 1st-6th embodiment demonstrated the light emitting diode element light-emitted in an ultraviolet wavelength range (deep ultraviolet wavelength range) as an example of a light emitting diode element, this invention is not limited to this, but ultraviolet (depth A light emitting element that emits light in a wavelength region other than (ultraviolet) can also be used.

  In the first embodiment, an example in which a nitride semiconductor light emitting element is mounted on a can-type package has been described. However, the present invention is not limited to this, and a nitride semiconductor may be used in a package other than the package described in the above embodiment. A light emitting element can also be mounted. Also, the nitride semiconductor light emitting elements shown in the second to sixth embodiments can be configured in a semiconductor optical device by being mounted on a package, as in the first embodiment.

  Moreover, in the said embodiment, although the template board | substrate with which the 1 layer or 2 layer nitride semiconductor layer was formed on the board | substrate was demonstrated, this invention is not restricted to this, A several layer more than 3 layers on a board | substrate is demonstrated. The template substrate can also be configured by forming a nitride semiconductor layer. At this time, the nitride semiconductor layers formed on the substrate may have different compositions or the same composition.

  Embodiments obtained by appropriately combining the techniques (configurations) disclosed above are also included in the technical scope of the present invention.

10 Nitride semiconductor substrate (semiconductor layer having a growth surface)
10a, 20a, 310a, 320a, 710a,
720a, 730a Growth surface 20 Nitride semiconductor layer (semiconductor layer having a growth surface)
21 GaN layer (semiconductor layer having a growth surface)
30 Template substrate 110 n-type AlInGaN layer, n-type AlGaN layer 120 active layer 120a quantum well layer 120b barrier layer 130 carrier block layer 140 p-type AlInGaN layer, p-type AlGaN layer 150 p-type contact layer 160 p-side electrode 170 n-side electrode 200 Nitride semiconductor layer, layer structure 210 n-side nitride semiconductor layer 220 p-side nitride semiconductor layer 300 semiconductor substrate 310 base substrate (semiconductor layer having a growth surface)
320 Nitride semiconductor layer (semiconductor layer having a growth surface)
400 Nitride semiconductor layer (semiconductor layer having a growth surface)
500, 600, 700, 800,
850, 860, 900 Nitride semiconductor light emitting device 710 Underlying substrate 720 First nitride semiconductor layer (semiconductor layer having a growth surface)
730 Second nitride semiconductor layer (semiconductor layer having a growth surface)
910 AlN layer 1000 Semiconductor optical device

Claims (22)

A semiconductor layer having a growth surface and made of a nitride semiconductor;
A nitride semiconductor layer including an active layer formed on a growth surface of the semiconductor layer and having a quantum well structure;
The active layer includes a quantum well layer made of a nitride semiconductor containing Al,
The growth surface of the semiconductor layer is composed of a plane having off-angles in the a- axis direction and the c- axis direction with respect to the m-plane , and the off-angle in the a-axis direction is greater than the off-angle in the c-axis direction. A nitride semiconductor device characterized by being large.   2. The nitride semiconductor device according to claim 1, wherein an off angle in the a-axis direction and an off angle in the c-axis direction are each greater than 0.1 degree.   3. The nitride semiconductor device according to claim 1, wherein an off angle in the a-axis direction is greater than 0.1 degree and equal to or less than 10 degrees.   4. The nitride semiconductor device according to claim 1, wherein an off angle in the a-axis direction is greater than 1 degree and 10 degrees or less. 5. The quantum well layer is made of a semiconductor represented by a composition formula of Al _x1 In _y1 Ga _{1 -x1-y1} N (0 <x1 ≦ 1, 0 ≦ y1 ≦ 1). The nitride semiconductor device according to any one of 1 to 4.   6. The nitride semiconductor device according to claim 5, wherein an Al composition ratio X1 of the quantum well layer is in a range of 0.15 ≦ x1 ≦ 0.90.   7. The nitride semiconductor device according to claim 5, wherein an In composition ratio y1 of the quantum well layer is in a range of 0.00 ≦ y1 ≦ 0.12. The semiconductor layer is made of a nitride semiconductor containing Al,
The Al composition ratio of the semiconductor layer is larger than the Al composition ratio of the quantum well layer, and the Al composition ratio is 0.20 or more and 1.00 or less. The nitride semiconductor device according to any one of the above. The active layer includes a barrier layer made of a semiconductor represented by a composition formula of Al _x2 In _y2 Ga _1-x2-y2 N (0 <x2 ≦ 1, 0 ≦ y2 ≦ 1),
The nitride semiconductor device according to claim 1, wherein an Al composition ratio x2 of the barrier layer is larger than an Al composition ratio of the quantum well layer.   10. The nitride semiconductor device according to claim 9, wherein an Al composition ratio x2 of the barrier layer is in a range of 0.20 ≦ x2 ≦ 1.00. In the case where the quantum well layer is composed of a semiconductor represented by a composition formula of Al _x1 In _y1 Ga _{1 -x1-y1} N (0 <x1 ≦ 1, 0 ≦ y1 ≦ 1),
The In composition ratio y2 of the barrier layer is smaller than the In composition ratio y1 of the quantum well layer and is in the range of 0.00 ≦ y2 ≦ 0.08. The nitride semiconductor device described.   The nitride semiconductor device according to any one of claims 9 to 11, wherein the barrier layer is made of AlGaN or AlInGaN.   The nitride semiconductor device according to claim 1, wherein the quantum well layer is made of AlGaN or AlInGaN.   The nitride semiconductor device according to claim 1, wherein an AlN layer is formed on the growth surface of the semiconductor layer so as to be in contact with the growth surface. The nitride semiconductor layer formed on the growth surface of the semiconductor layer includes an n-side nitride semiconductor layer formed on the semiconductor layer side with respect to the active layer, and the n-side nitridation with respect to the active layer. A p-side nitride semiconductor layer formed on the opposite side of the oxide semiconductor layer,
The nitride semiconductor device according to claim 1, wherein the n-side nitride semiconductor layer does not include a GaN layer.   The nitride semiconductor device according to claim 1, wherein a wavelength of light emitted from the active layer is 240 nm or more and 360 nm or less.   The nitride semiconductor device according to claim 16, wherein the wavelength of light emitted from the active layer is 260 nm or more and 300 nm or less.   The nitride semiconductor device according to claim 1, wherein the semiconductor layer having the growth surface is made of any one of AlGaN, AlInGaN, and AlN. Comprising a substrate constituting the semiconductor layer having the growth surface;
The nitride semiconductor device according to any one of claims 1 to 18, wherein the substrate is composed of any one of an AlGaN substrate, an AlInGaN substrate, and an AlN substrate. Comprising a substrate constituting the semiconductor layer having the growth surface;
The nitride semiconductor device according to claim 1, wherein the substrate is made of a GaN substrate. A template substrate having the semiconductor layer formed on a base substrate;
The nitride semiconductor device according to claim 1, wherein the nitride semiconductor layer including the active layer is formed on the template substrate.   A semiconductor optical device comprising the nitride semiconductor element according to claim 1.

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